1. Field of Invention
This invention relates to a sampling head provided in a high frequency device, such as a sampling oscilloscope; and more particularly, to such a sampling head which is capable of high speed measurement and which can be readily miniaturized.
2. Description of the Prior Art
A sampling head, such as disclosed in U.S. Pat. No. 3,629,731, is used in a sampler which functions to gather a measured high frequency signal at a predetermined cycle and to re-synthesize the gathered data at a low frequency. The sampling head, used for the sampler, is an important element of a high frequency device, such as a network analyzer or a waveform analyzer.
In the sampling head, a measurement frequency band is determined by a gate time of a diode bridge included therein. In order to gate the diode bridge, an impulse, also called a strobe pulse, is used. In the conventional apparatus, a step recovery diode (SRD) is used for a high frequency strobe pulse generator. Also, GaAs Schottky barrier diodes (SBD) are used for the diode bridge. A strobe command pulse, used for gating the diode bridge, is produced by an outside device, and is applied to the diode bridge through a bonding material.
The above conventional device has many problems. For example, the upper limit of the sampling frequency is determined by the pulse width of the strobe pulse. However, when the SRD is used as a strobe pulse generator, the pulse width can not be made to be less than 30 ps . Thus, the frequency band is limited. Also, since the SRD involves a quantity of jitters, time resolution is not improved. Moreover, a large power (about 100 Vpp and 1 A) is necessary to drive the SRD, and the output pulse includes large noise components.
In case a GaAs Schottky barrier diode is used as the diode bridge, the characteristic (ON voltage V.sub.F) is not controlled. Thus, desired performance is not obtained. Further, the strobe pulse used for gating the diode bridge is applied from the outside device through a bonding material, and thus, the frequency band is limited by the loss at the bonding or connecting part.